When building an aircraft, it is known to begin by making a lower section of a segment of the fuselage. This lower section constituting the bottom portion of the segment is upwardly open. The portion of the floor that occupies this segment is then inserted through the upward opening. Thereafter, the various systems and members that are to be fastened to the fuselage and to the floor are mounted in the assembly. These may be hydraulic or pneumatic members (compressed air or air conditioning ducts, water ducts, refrigeration ducts, oxygen ducts), electric cables, fire extinguisher circuit elements, or indeed ducts for on-board communications networks. These various members are fastened to the underside of the floor or to the fuselage, e.g. in the zones referred to as “triangular” zones because of their shape, i.e. the zones that are close to the junction between the floor and the fuselage.
Nevertheless, that method of mounting presents drawbacks. Thus, it is necessary to wait until the structure (the fuselage and the floor) have finished being assembled before beginning to put the systems into place, thereby lengthening the overall time required to build the aircraft. Furthermore, introducing systems into the triangular zones raises ergonomic problems for operators. Those zones constitute a confined space that is of difficult access, obliging operators to work in crouching or even prone positions, particularly in fuselages of small diameter.